No till and cover cropping for vegetables

by Tamara Scully

Soil health happens in a
cumulative manner, year after year, when attention is paid to sequestering
carbon. Carbon helps to add stability to soil aggregates and to enhance soil
water retention and soil nutrient retention. It is part of a healthy ecosystem
for soil microbiota.

When using no till in
conjunction with cover crops, “all of these come together and integrate,” Dr.
Gladis Zinati, director of the Vegetable Systems Trial at the Rodale Institute,
said at during a presentation at the recent No-till and Cover Crops conference
hosted by the non-profit North Jersey Resource Conservation and Development.

Over the past 50 years,
conventional farming practices have led to decreases in the levels of vitamins,
minerals and protein in our vegetable crops. While yields may have increased,
the nutrient density of those crops has significantly declined. Practices such
as tillage and plowing release carbon from the soil, adding oxygen which
microbes digest and release as carbon dioxide. These practices lead to
decreases in overall soil health, Zinati said, and contribute to the nutrient
decline seen in vegetables today.

By using no-till practices,
combined with cover crops, “you are sequestering the carbon back to your soil.
You are building your soil organic matter,” she said. But “no-till in vegetable
is so difficult to do 100 percent.”

No matter the crop, there are a
lot of factors that need to be successfully implemented to make no-till
production of any crop successful. The right cover crop – “not allelopathic to
the cash crop” – a good crop rotation schedule, the right cultivar selection,
good pest management and the best management of crop residue all have to work
together, Zinati explained.

Examining Nutrition

The objective of the Vegetable
Systems Trial is to explore the link between soil health and human health by
measuring the nutrient density of vegetables grown in a variety of farming
systems in side-by-side comparisons. They will be analyzing root, fruit and
leaf crops grown in conventional, organic manure-based and organic legume-based
growing systems. Each system will be further divided into tillage, no-till and
rotational tillage plots.

Researchers will be collecting data
on the nutrient density of the food as well as soil health, insect and weed
pressure, drought resilience and profitability. The study, which began in 2017,
will run for 20 years.

In 2017, research on the striped
cucumber beetle was conducted at Rodale Institute, comparing plastic mulch to a
rolled oats mulch to determine if there was any impact on the insect. No
statistical difference was seen between the presence of the pest grown on the
crop in the plastic or the living mulch system. However, the rolled oats mulch
produced a cucumber crop with higher nutrient levels.

“It’s really helping other
things in the plant,” Zinati said of the use of the rolled oats cover crop
system. Polyphenol levels in the crop grown in the rolled oats were higher than
in the crop grown on plastic. Plants use polyphenols to deter pathogens and
insects.

Further research examined the
difference in nutrient content in winter squash grown under organic conditions
using conventional tillage and two no-till organic systems. In the first
no-till system, the crop was planted with two feet wide rows, using a
walk-behind roller crimper, while in the second the rows were 10 feet apart,
wide enough to accommodate the use of a tractor-mounted roller crimper for
cover crop termination.

After harvest, levels of
carotenoids, including lutein and alpha-carotene, which are important
phytochemicals for human health, were assessed. Researchers also measured
levels after being in storage to determine what effect time in storage would
have.

In both no-till systems, the
levels of the carotenoids increased significantly after 30 and 60 days of
storage. The squash grown in the tractor-pulled roller crimper system had the
highest levels of carotenoids. The tillage-grown squash not only had the lowest
levels of these important phytochemicals, but the levels decreased in storage
over time.

The results demonstrate that
differences in crop management can impact the nutrient properties of the crop
itself. Further large-scale studies to examine how and why these changes in
phytochemical levels occur will be conducted.

Having the right equipment, such
as roller crimpers, which allow farmers to terminate a cover crop without
chemicals or tillage is crucial to cover cropping and no till success. The
biomass produced by the cover crop is also important. The residue has to allow
planting into it, but also has to be sufficient to suppress weed growth.

Depending on the species of
cover crop chosen, the amount of nitrogen fixed will vary. After termination,
time for the cover crop to release nitrogen is key. The amount of soil
fertility needed will depend on the requirements of the cash crop.

A tillage radish crop provides
“biological tillage,” she said, and takes the nutrients from the soil and moves
them up. The tillage radish does not overwinter, so in the spring,
transplanting vegetables into this soil allows the crop to access the now-available
nutrients.

Zinati explained there are four
stages to the transition from tillage to no-till practices using cover crops.
The first five years are needed to start to build the soil. Years six through
10 will see increases in soil organic matter, increases in soil structure and
in microbial activity. The next 10 years will accumulate carbon reserves in the
soil, and the enhanced nutrient cycling that occurs with high levels of soil
health means “you will see the evidence,” she said.

From 20 years onward, it’s a
matter of maintaining optimal soil health. Adding nutrients back to the soil
and not letting the crops deplete fertility while continuing to sequester
carbon and feed the soil microbiota will keep soil health and productivity
optimized, and will translate into nutrient dense crops.